This invention relates to a suspension unit and particularly, but not exclusively, relates to a suspension unit for use on a tracked vehicle.
A tracked vehicle has a track extending around a series of track guide wheels. At least some of the guide wheels support the weight of the vehicle hull on the section of the track which is in contact with the ground. In this specification, the expression “hull” is used to refer to the main body of the vehicle. The hull serves the same purpose as the chassis of a conventional vehicle, whether or not the chassis is constituted wholly or partially by the bodywork of the vehicle. Consequently, in the context of the present invention, the word “hull” is considered to be equivalent to a vehicle chassis.
The track guide wheels which support the weight of the vehicle on the ground need to be connected to the vehicle hull by a suspension arrangement which enables the track guide wheel to move up and down relative to the hull.
A suspension system is known in which the suspension system comprises an arm which is pivotable relative to the hull about a pivot axis. A wheel-supporting shaft is carried by the arm at a position away from the pivot axis, for supporting a track guide wheel. A resilient damping arrangement is accommodated within the arm for providing damped resilient resistance to deflection of the arm away from a static position in a direction corresponding to movement of the hull towards the ground.
At least one displaceable element of the resilient damping arrangement is connected to the hull via a connecting rod that is connected for rotation with a crank pin. The crank pin is carried in a hub that is rigidly connected to the hull of the vehicle. In conventional systems, the crank pin is supported for rotation within the hub by two simple cylindrical bearing shells spaced equally in the axial direction about a central region, over which the connecting rod is connected to the crank pin. This connection is achieved by an end of the connecting rod completely encircling the crank pin. Load is transmitted from the connecting rod through the crank pin and is reacted through the bearing shells to the surrounding structure. It is essential that the bearing shells of such a system are sufficiently large to achieve unit loading of the bearing shells that is within the load capabilities of the bearing shell material. In addition, the crank pin must be sufficiently large in diameter to withstand the bending loads applied when the force transmitted through the connecting rod is reacted by the bearing shells.
In certain applications, the space claim of each individual component is highly restricted. In addition, the load patterns experienced by the components may be substantially consistent, for example compression only loading through the connecting rod. In such applications in particular, there exists a need to provide a reduced diameter crank pin while still maintaining crank pin integrity and unit bearing loading within the bearing material rated capabilities.